Optimising the throughput performance for wireless networks is one of the challenging tasks in the objectives of communication engineering, since wireless channels are prone to errors due to path losses, random noise, and fading phenomena. The transmission errors will be worse in a multihop scenario due to its accumulative effects. Network Coding (NC) is an elegant technique to improve the throughput performance of a communication network. There is the fact that the bit error rates over one modulation symbol of 16- and higher order- Quadrature Amplitude Modulation (QAM) scheme follow a certain pattern. The Scattered Random Network Coding (SRNC) system was proposed in the literature to exploit the error pattern of 16-QAM by using bit-scattering to improve the throughput of multihop network to which is being applied the Random Linear Network Coding (RLNC). This thesis aims to improve further the SRNC system by using Forward Error Correction (FEC) code; the proposed system is called Joint RLNC and FEC with interleaving. The first proposed system (System-I) uses Convolutional Code (CC) FEC. The performances analysis of System-I with various CC rates of 1/2, 1/3, 1/4, 1/6, and 1/8 was carried out using the developed simulation tools in MATLAB and compared to two benchmark systems: SRNC system (System-II) and RLNC system (System- III). The second proposed system (System-IV) uses Reed-Solomon (RS) FEC code. Performance evaluation of System IV was carried out and compared to three systems; System-I with 1/2 CC rate, System-II, and System-III. All simulations were carried out over three possible channel environments: 1) AWGN channel, 2) a Rayleigh fading channel, and 3) a Rician fading channel, where both fading channels are in series with the AWGN channel. The simulation results show that the proposed system improves the SRNC system. How much improvement gain can be achieved depends on the FEC type used and the channel environment. / Indonesian Government and the University of Bradford

Wireless Sensor Networks (WSNs) that use tiny wireless devices capable of communicating, processing, and sensing promise to have applications in virtually all fields. Smart homes and smart cities are just few of the examples that WSNs can enable. Despite their potential, WSNs suffer from reliability and energy limitations. In this study, we address the problem of designing Distributed Data Storage Systems (DDSSs) for WSNs using decentralized erasure codes. A unique aspect of WSNs is that their data is inherently decentralized. This calls for a decentralized mechanism for encoding and decoding. We propose a distributed data storage framework to increase data survivability in WSNs. The framework utilizes Decentralized Erasure Codes for Data Survivability (DEC-DS) which allow for determining the amount of redundancy required in both hardware and data to allow sensed data to survive failures in the network. To address the energy limitations, we show two approaches to implement the proposed solution in an energy efficient manner. The two approaches employ Random Linear Network Coding (RLNC) to exploit coding opportunities in order to save energy and in turn prolong network life. A routing based scheme, called DEC Encode-and-Forward (DEC-EaF), applies to networks with routing capability, while the second, DEC Encode-and-Disseminate (DEC-EaD), uses a variation of random walk to build the target code in a decentralized fashion. We also introduce a new decentralized approach to implement Luby Transform (LT)-Codes based DDSSs. The scheme is called Decentralized Robust Soliton Storage (DRSS) and it operates in a decentralized fashion and requires no coordination between sensor nodes. The schemes are tested through extensive simulations to evaluate their performance. We also compare the proposed schemes to similar schemes in the literature. The comparison considers energy efficiency as well as coding related aspects. Using the proposed schemes can greatly improve the reliability of WSNs especially under harsh working conditions. / Thesis (Ph.D, Electrical & Computer Engineering) -- Queen's University, 2013-09-30 22:43:04.509

Network coding (NC) has gained much research attention as a potential candidate to solve the demand for higher spectral e ciency of modern wireless communications. Many research papers have investigated the performance of NC-aided networks such as throughput and outage capacity. However, the analysis of NC in practical systems where NC is combined with other techniques such as channel coding is still immature to fully understand its potential performance. In this thesis, we aim to design high performance receivers and analyze its performance for network-coded cooperative networks in practical scenarios. Firstly, we propose two Iterative Network/Channel Decoding (INCD) algorithms for the Multiple-Access Relay Channel (MARC) with two notable relaying schemes named Decode-and-Forward (DF) and Demodulate-and-Forward (DMF). The INCD algorithm operates based on turbo-like decoding methods and reduces the impact of the error propagation problem with the aid of a channel-aware receiver design. Both perfect Channel State Information (CSI) and imperfect CSI at the receiver side are investigated. We propose a practical method that forwards the quantized version of the relay decoding errors to the destination. It is shown that the proposed algorithms achieve full diversity gain and signi cantle outperforms solutions which do not take care of error propagation. We also show that the number of pilot symbols a ects only the coding gain but has a negligible impact on the diversity order, while the quantization level a cts both the diversity and coding gain. Secondly, we propose a Near Optimal Joint Network/Channel Decoding (NOJNCD) algorithm for the MARC that allows to analyze the system Bit Error Rate (BER). The NOJNCD algorithm performs network decoding and channel decoding in one decoding step of the super code, which comprises of all trellis states of individual code at the sources via NC. Furthermore, NC combined with Relay Selection (RS) is considered and the achievable diversity order is studied with the aid of outage analysis. We analytically show that Single Relay Selection (SRS) always achieves a diversity order two and Multiple Relay Selection (MRS) can achieve full diversity gain only when the number of selected relays exceeds the number of the sources. Last but not least, we propose a so-called partial relaying protocol to improve the spectral e ciency for channel coding assisted relay networks. Closed-form expression of the BER and the system diversity order are computed for partial relaying. We show, by analysis and simulations, that with a proper Convolutional Code (CC), partial relaying can achieve full diversity gain and same coding gain as the classical (full) relaying protocol in nite signal-to-noise ratio region while it obtains a better spectrum usage. Moreover, we propose a new protocol based on partial relaying in opportunistic relaying cooperative networks and show that this protocol signi cantly outperforms the NC-based cooperation in some circumstances.

Cooperative communications by pooling available resources—for example, power and bandwidth—across the network, is a distributed solution for providing robust wireless transmission. Motivated by contemporary applications in multi-hop transmission and ad hoc networks, the classical three-node relay channel (RC) consisting of a source–destination pair and a relay node has received a renewed attention. One of the crucial aspects of the communication over relay networks (RNs) is the design of proper relaying protocols; that is, how the relay should take part in the transmission to meet a certain quality of service. In this dissertation, we address the design of reliable transmission strategies and quantification of the associated transmission rates over RNs. We consider three canonical examples of RNs: the classical RC, the multiple-access RC (MARC) and the two-way RC.We also investigate the three-node RC and MARC with state. The capacity of the aforementioned RNs is an open problem in general except for some special cases. In the thesis, we derive various capacity bounds, through which we also identify the capacity of some new classes of RNs. In particular, we introduce the class of state-decoupled RNs and prove that the noisy network coding is capacity achieving under certain conditions. In the thesis, we also study the effect of the memory length on the capacity of RNs. The investigated relaying protocols in the thesis can be categorized into two groups: protocols with a finite relay memory and those with infinite relay memory requirement. In particular, we consider the design of instantaneous relaying (also referred to as memoryless relaying) in which the output of the relay depends solely on the presently received signal at the relay. For optimizing the relay function, we present several algorithms constructed based on grid search and variational methods. Among other things, we surprisingly identify some classes of semi-deterministic RNs for which a properly constructed instantaneous relaying strategy achieves the capacity. We also show that the capacity of RNs can be increased by allowing the output of the relay to depend on the past received signals as well the current received signal at the relay. As an example, we propose a hybrid digital–analog scheme that outperforms the cutset upper bound for strictly causal relaying. / <p>QC 20110909</p>

耐延遲網路(Delay Tolerant Networks)上的路由協定可以區分為兩大類:flooding-based protocols 跟forwarding-based protocols。網路編碼(Network Coding)是一種編碼技術可以提高訊息傳輸的可靠度；並且運作時不需要知道整體網路的拓樸資訊。 我們提出的演算法結合了flooding-based protocols 跟forwarding-based protocol特性，最主要的概念是讓訊息不是被傳送給每一個節點，而是傳送給朝向目的地或是接近目的地的節點。當節點相遇時，我們的方法會利用節點的路徑、移動方向與速度去預測到達目的地的機率。同時我們利用網路編碼的技巧傳送編碼後的資料來代替訊息的片段，來避免重複傳送多餘的訊息；並讓通訊更加可靠。根據實驗模擬的結果，我們的機制有較好的效能，特別是在頻寬的使用上。 / The routing protocols of delay tolerant networks could be divided in two categories: flooding-based protocols and forwarding-based protocols. Network coding is an encoding technique that could make data transmission more reliable. It operates without the needed of information about the network topology. We proposed a routing protocol integrating the characteristic of flooding-based protocol and forwarding-based protocol. The main idea of our protocol is to let message would not be flooded to every node but to the nodes moving toward or moving closer to destination. When nodes contact with each other, our approach will use the path of node, node’s moving direction and its velocity to estimate the probability to reach the destination of message. At the same time, we exploit network coding to transmit coded block instead of message fragment in order to avoid sending redundant replication, make data transmit more reliable and more robust to packet losses or delays. From the result of simulation, we could see that our protocol have a higher performance especially in the bandwidth consumption compared to other protocols.

In the context of error control in random linear network coding, it is useful to construct codes that comprise well-separated collections of subspaces of a vector space over a finite field. This thesis concerns the construction of non-constant-dimension projective space codes for adversarial error-correction in random linear network coding. The metric used is the so-called injection distance introduced by Silva and Kschischang, which perfectly reflects the adversarial nature of the channel. A Gilbert-Varshamov-type bound for such codes is derived and its asymptotic behaviour is analysed. It is shown that in the limit as the ambient space dimension approaches infinity, the Gilbert-Varshamov bound on the size of non-constant-dimension codes behaves similar to the Gilbert-Varshamov bound on the size of constant-dimension codes contained within the largest Grassmannians in the projective space. Using the code-construction framework of Etzion and Silberstein, new non-constant-dimension codes are constructed; these codes contain more codewords than comparable codes designed for the subspace metric. To our knowledge this work is the first to address the construction of non-constant-dimension codes designed for the injection metric.

In the context of error control in random linear network coding, it is useful to construct codes that comprise well-separated collections of subspaces of a vector space over a finite field. This thesis concerns the construction of non-constant-dimension projective space codes for adversarial error-correction in random linear network coding. The metric used is the so-called injection distance introduced by Silva and Kschischang, which perfectly reflects the adversarial nature of the channel. A Gilbert-Varshamov-type bound for such codes is derived and its asymptotic behaviour is analysed. It is shown that in the limit as the ambient space dimension approaches infinity, the Gilbert-Varshamov bound on the size of non-constant-dimension codes behaves similar to the Gilbert-Varshamov bound on the size of constant-dimension codes contained within the largest Grassmannians in the projective space. Using the code-construction framework of Etzion and Silberstein, new non-constant-dimension codes are constructed; these codes contain more codewords than comparable codes designed for the subspace metric. To our knowledge this work is the first to address the construction of non-constant-dimension codes designed for the injection metric.

Wireless technology has become an increasingly popular way to gain network access. Wireless networks are expected to provide efficient and reliable service and support a broad range of emerging applications, such as multimedia streaming and video conferencing. However, limited wireless spectrum together with interference and fading pose signi cant challenges for network designers. The novel technique of network coding has a significant potential for improving the throughput and reliability of wireless networks by taking advantage of the broadcast nature of wireless medium. Reverse carpooling is one of the main techniques used to realize the benefits of network coding in wireless networks. With reverse carpooling, two flows are traveling in opposite directions, sharing a common path. The network coding is performed in the intermediate (relay) nodes, which saves up to 50% of transmissions. In this thesis, we focus on the scheduling at the relay nodes in wireless networks with reverse carpooling. When two packets traveling in opposite directions are available at the relay node, the relay node combines them and broadcasts the resulting packet. This event is referred to as a coding opportunity. When only one packet is available, the relay node needs to decide whether to wait for future coding opportunities, or to transmit them without coding. Though the choice of holding packets exploits the positive aspects of network coding, without a proper policy in place that controls how long the packets should wait, it will have an adverse impact on delays and thus the overall network performance. Accordingly, our goal is to find an optimal control strategy that delicately balances the tradeoff between the number of transmissions and delays incurred by the packets. We also address the fundamental question of what local information we should keep track of and use in making the decision of of whether to transmit uncoded packet or wait for the next coding opportunity. The available information consists of queue length and time stamps indicating the arrival time of packets in the queue. We could also store history of all previous states and actions. However, using all this information makes the control very complex and so we try to find if the overhead in collecting waiting times and historical information is worth it. A major contribution of this thesis is a stochastic control framework that uses state information based on what can be observed and prescribes an optimal action. For that, we formulate and solve a stochastic dynamic program with the objective of minimizing the long run average cost per unit time incurred due to transmissions and delays. Subsequently, we show that a stationary policy based on queue lengths is optimal, and the optimal policy is of threshold-type. Then, we describe a non-linear optimization procedure to obtain the optimal thresholds. Further, we substantiate our analytical ndings by performing numerical experiments under varied settings. We compare systems that use only queue length with those where more information is available, and we show that optimal control that uses only the queue length is as good as any optimal control that relies on knowing the entire history.

Mobile Ad hoc NETworks (MANETs) aim at making communication between mobile nodes feasible without any infrastructure support. Sparse MANETs fall into the class of Delay Tolerant Networks which are intermittently connected networks and where there is no contemporaneous end-to-end path at any given time. We first, propose a new reliable transport scheme for DTNs based on the use of ACKnowledgments and random linear coding. We model the evolution of the network under our scheme using a fluid-limit approach. We optimize our scheme to obtain mean file transfer times on certain optimal parameters obtained through differential evolution approach. Secondly, we propose and study a novel and enhanced ACK to improve reliable transport for DTNs covering both unicast and multicast flows. We make use of random linear coding at relays so that packets can reach the destination faster. We obtain reliability based on the use of so-called Global Selective ACKnowledgment. We obtain significant improvement through G-SACKs and coding at relays. Finally, we tackle the problem of estimating file-spread in DTNs with direct delivery and epidemic routing. We estimate and track the degree of spread of a message in the network. We provide analytical basis to our estimation framework alongwith insights validated with simulations. We observe that the deterministic fluid model can indeed be a good predictor with a large of nodes. Moreover, we use Kalman filter and Minimum- Mean-Squared-Error (MMSE) to track the spreading process and find that Kalman filter provides more accurate results as compared to MMSE

In this thesis we deal with the application of Network Coding to guarantee the Quality of Service (QoS) for wireless multi-hop networks. Since the medium is shared, wireless networks suffer from the negative interference impact on the bandwidth. It is thus interesting to propose a Network Coding based approach that takes into account this interference during the routing process. In this context, we first propose an algorithm minimizing the interference impact for unicast flows while respecting their required bandwidth. Then, we combine it with Network Coding to increase the number of admitted flows and with Topology Control to still improve the interference management. We show by simulation the benefit of combining the three fields: Network Coding, interference consideration and Topology Control. We also deal with delay management for multicast flows and use the Generation-Based Network Coding (GBNC) that combines the packets per blocks. Most of the works on GBNC consider a fixed generation size. Because of the network state variations, the delay of decoding and recovering a block of packets can vary accordingly degrading the QoS. To solve this problem, we propose a network-and content-aware method that adjusts the generation size dynamically to respect a certain decoding delay. We also enhance it to overcome the issue of acknowledgement loss. We then propose to apply our approach in a Home Area Network for Live TV and video streaming. Our solution provides QoS and Quality of Experience for the end user with no additional equipment. Finally, we focus on a more theoretical work in which we present a new Butterfly-based network for multi-source multi-destination flows. We characterize the source node buffer size using the queuing theory and show that it matches the simulation results.